A dual-template strategy to engineer hierarchically porous Fe–N–C electrocatalysts for the high-performance cathodes of Zn–air batteries

Abstract

Extensive efforts have been devoted to active site designing for non-precious metal electrocatalysts; however, the porous structure engineering has been less emphasized, particularly for catalysts for gas diffusion electrodes, e.g., the cathode (oxygen reduction reaction, ORR) of Zn–air batteries. The desired porous structure is not only important for exposing high-density active sites but also beneficial for boosting mass transfer. Here, a dual-template strategy is proposed for constructing hierarchically porous structural Fe–N–C catalysts with dense active Fe–N_x moieties for the cathode of Zn–air batteries. The dual ZnCl₂ and MgO hard templates jointly promote the formation of hierarchically interconnected carbon networks. The experimental results indicated both significantly improved active site accessibility and mass transfer, reasonably leading to enhanced ORR activity in conventional three-electrode cells. Particularly, it is deduced that the microporous structure is beneficial for dense active Fe–N_x moieties, while the ultra-macroporous structure is conducive to mass transfer during the ORR process. We further applied this dual-template-mediated catalyst in a real-world liquid Zn–air battery, which presents a high open-circuit voltage of 1.48 V and a remarkable energy density of 952.8 W h kg_Zn⁻¹. Such robust battery performance is among the best compared with reported Zn–air batteries using non-precious metal catalysts. Particularly, a peak power density of 116.8 mW cm⁻² is achieved in an all-solid-state Zn–air battery.